A man's survival often depended on whether or not he had a reliable firelock close at hand. When out hunting, he used it to obtain food for himself and his family. He might also call on his firelock to defend himself from dangerous animals or unfriendly natives. There were plenty of both!
This is a Long Land Pattern (or First Model) English Brown Bess Musket, with bayonet. These military firelocks, and their later variants, were built for use by the British Army beginning in about 1728, and were their standard military firelock for over 100 years. As the older weapons were replaced by newer versions, they were often sold to members of the local militias. Many men carried their firelocks with them when they left their service in the British Army.
There were also civilian maker who turned out very serviceable smoothbore fowlers and hunting guns, and during the early part of the 18th century, that's what most frontiersmen carried. Rifles were just coming on the scene in the mid to late 1740's, and then mostly from German immigrant gunbuilders who modeled them after their Jaeger rifles. Slowly a mix of the Jaeger style rifle and the colonial long guns evolved into what became the American longrifle.
A reproduction of the Edward Marshall Rifle of "Walking Purchase" fame
At first, only people of means who had the fortune to be in an area where these German gunbuilders were located would have had access to the rifled firelocks. As more and more were made, and the concept caught on, their availability and popularity spread. Even so, it was after the American Revolution that the rifle became a commonly used firelock.